I don't think there is an official way to change fonts.
But there was an unofficial trick that worked for me at least on earlier AGS games.
You can try if you want! Just choose some other font you like, place it in the game directory - and name it agsfnt1.ttf and/or agsfnt2.ttf, agsfnt3.ttf, agsfnt4.ttf. One of those names could work (or not).